This invention is related to a machine capable of grinding and polishing a plurality of disc-shaped work pieces simultaneously, and a method for using the machine to impart a circumferential pattern on the plurality of disc-shaped work pieces.
Computer memory discs are typically highly polished articles which must meet rigorous quality specifications. Any flaw on the surface of a hard disc will result in the permanent loss of at least a portion of the memory capacity of that disc. The grinding and polishing of such hard discs by machines of the prior art have resulted in hard discs having radial, or rose petal patterns in which there are small grooves running from the center of the disc to the outside radius of the disc, or in discs with spiral patterns where the spiral begins in the center of the disc and spirals until it ends at the outside of the hard disc. Flaws in the radial or spiral impressions may cut across large lateral portions of the disc resulting in the loss of a very substantial amount of potential memory space, making the disc unusable.
Newer machines may impart a circumferential pattern on the hard disc. The desired circumferential pattern consists of a series of concentric rings beginning in the center of the hard disc and radiating towards the outside edge of the hard disc. A flaw in a concentric ring of the circumferential pattern will result in the loss of only a small portion of the hard disc memory capacity, namely the memory capacity defined by the flawed concentric circle. Present methods of imparting a circumferential pattern on a hard disc are time consuming because they are slow, and because only one disc at a time can be machined.